Hazardous or volatile materials such as gasoline are primarily transported in bottom loading cargo tanks. Typically, each cargo tank has four or five compartments with an external loading/unloading line (hereinafter "wet line") mounted at the bottom center of each compartment. The cargo tank is loaded with liquid material which passes through the wet lines and into the compartments. After each compartment of the cargo tank is filled, a residual amount of between about- four and about ten gallons of the hazardous liquid material may remain in the corresponding wet line. Because the liquid material contained in the wet lines after loading has been metered and sold to the customer and because there are no convenient ways to remove this residual liquid material yet still deliver it to the customer, the current practice is to allow the liquid material to remain in the cargo tank wet lines during transportation.
Bottom loading cargo tank wet lines are particularly vulnerable to damage in traffic accidents, since the impact of an automobile will occur at the lower portion of the cargo tank (hereinafter "under-ride accidents"). In addition, bottom loading cargo tank wet lines are currently designed to fail upon impact during under-ride accidents in order to maintain the integrity of the tank compartments and prevent the release of the entire content of the cargo tank. Therefore, the transportation of hazardous materials in bottom loading cargo tanks presents the inherent risk of releasing hazardous materials from the cargo tank wet lines upon impact during an under-ride accident. Thus, there exists a pressing need to eliminate this inherent risk of transporting hazardous materials in bottom loading cargo tanks.
Presently, there is no known reliable technique to safeguard bottom loading cargo tank wet lines from rupturing upon impact and releasing the hazardous material. Previously, a proposal was made to construct a barrier or shield around the wet lines to protect them from breakage upon impact. However, the risk of breakage still exists if the impact is greater than the barrier can withstand. Further, a study by the American Petroleum Institute (the "A.P.I.") has suggested that efforts to safeguard bottom loading cargo tank wet lines with bottom damage protection structures are not cost effective. More recently, the A.P.I. has proposed conducting a study to identify feasible solutions to the problem of wet line breakage. Thus, there exists a compelling and industry recognized need for a reliable and cost effective method to eliminate the risk of carrying hazardous material in bottom loading cargo tanks.